The present invention relates to an apparatus and a method for detecting, ascertaining the location of, or quantifying chemical species using selective chemical interaction and selective chemical detection. More particularly, the present invention relates to an apparatus and a method for in-situ detecting or quantifying chemical species using selective chemical interaction and detection of products of such chemical interaction and selectively spatially resolved chemical detection of analytes.
As industrial and commercial activities continue to accelerate, many manmade chemical species have found their way into the environment, heightening concern about human health and safety. Halogenated hydrocarbons that have been used as industrial solvents, medium for extraction of natural products, degreasing agents, dry cleaning fluids, refrigerants, fuel additives, fumigants, and intermediates for the synthesis of a multitude of other organic compounds have appeared in ground water at numerous locations. Other chemical compounds, such as explosives and rocket propellants, have contaminated soil at and migrated beyond manufacturing sites. Concern about the health effects of chemical compounds such as these in the environment has led to the quest for better methods for detecting and monitoring their presence. Many chemical species interact with other chemical compounds to yield products that have identifiable characteristics, providing reliable identification thereof. Detection methods for these products relying on these characteristics include optical (refractive index, scattering, etc.), spectroscopic (UV-visible (xe2x80x9cUV-VISxe2x80x9d) electronic absorbance, Raman, luminescence, infrared, near infrared), electrochemical, gravimetric, mass spectrometric, and other types of detection known in the art. Many colorless or optically transparent chemical species react with selected reagents to yield colored or fluorescent products, which can provide the basis for the detection of such chemical species.
One such method of detection is based on the reaction of halogenated hydrocarbons with pyridine or pyridine derivatives in an alkaline medium to yield red colored products in what has been commonly known as the Fujiwara reaction.
Many other compounds react with selected reagents to yield products that absorb electromagnetic (xe2x80x9cEMxe2x80x9d) radiation in the wavelength range from ultraviolet (xe2x80x9cUVxe2x80x9d) to infrared (xe2x80x9cIRxe2x80x9d). For example, some polynitroaromatic compounds react with ethylenediamine to yield products that absorb at wavelength of about 455 nm or about 530-560 nm.
The optical effects of selective chemical interaction have been incorporated in optical fibers for the determination of the location or the spatial distribution of selected chemical compounds by measuring the backpropagated EM radiation. Such method is known as xe2x80x9coptical time-domain reflectometryxe2x80x9d or xe2x80x9cOTDR.xe2x80x9d For example, a fiber-optic waveguide having an aluminosilica xerogel clad was used to detect the spatial distribution of quinizarin (1,4-dihydroxyanthraquinone) (C. A. Browne et al., xe2x80x9cIntrinsic Sol-Gel Clad Fiber-Optic Sensors With Time-Resolved Detection,xe2x80x9d Anal. Chem., Vol. 68, No. 14, 2289 (1996)). Quinizarin adjacent to the optical fiber sensor complexes with aluminum in the clad to yield a product that strongly absorbs EM radiation at wavelength of about 560 nm. Therefore, a measurement of the light intensity at wavelength of 560 nm and the arrival time at the detector of the return light of a pulse of light launched into the fiber-optic waveguide indicates the concentration and the location of quinizarin.
However, the basic OTDR method has several disadvantages that limit its appeal in chemical detection. The most important disadvantage is the low intensity of detected backpropagated radiation which can be 102-105 times weaker than the forward traveling pulse. As a result, recording a useful signal of backpropagated radiation requires sophisticated detection schemes, high-power lasers, and time-consuming signal-averaging techniques. Frequently, signal integration times are in the range of several tens of minutes and involve averaging 105-107 waveforms. Several methods have been devised and demonstrated to raise the levels of these signals. These methods include those based on pseudonoise, polarimetry, and nonlinear optical effects. Unfortunately, these techniques are limited to the use of single-mode optical fibers which are very difficult to implement for chemical detection.
Therefore, there is a continued need for simple apparatuses and convenient methods for detecting, determining the location or the spatial distribution of, and quantifying chemical species. It is also desirable to have such simple apparatuses and methods for readily implementing in the field.
The present invention provides an apparatus and a method for detecting the presence, determining the location or the spatial distribution, and quantifying an amount of at least one chemical species by allowing the chemical species to come into contact with a fluid medium spatially distributed in a defined container having a permeable wall with respect to the chemical species. The location or spatial distribution of the chemical species is thus determinable from the location of the sample of the fluid medium at the location within the container at which the contact occurs. In one preferred embodiment, the container is a capillary. The fluid medium can comprise at least one reagent with which the chemical species can undergo a selective chemical interaction after permeating the wall of the container. The apparatus and method of the present invention are easily implementable in the field. The term xe2x80x9cchemical interaction,xe2x80x9d as used herein, refers to a coupling via a formation of permanent or temporary bonds between the chemical species and a selected reagent to yield a product species. The term xe2x80x9cchemical interactionxe2x80x9d includes, but is not limited to, chemical reaction, formation of chemical complexes, hydrogen bonding, and hydration.
An apparatus of the present invention comprises (1) a capillary the wall of which is permeable to at least one chemical species to be detected; (2) a means for delivering at least one fluid medium into the space inside the capillary; and (3) a means for transferring a content of the capillary to a detector for detecting the at least one chemical species. The detector provided in an apparatus of the present invention is at least one that employs a sensor or a method of detection selected from the group consisting of optical (refractive index or light scattering), spectroscopic (UV-VIS electronic absorbance, Raman, luminescence, infrared, or near infrared), electrochemical, gravimetric, mass spectrometric, and other sensors or methods known in the art.
According to one embodiment of the present invention, an apparatus of the present invention comprises (1) a capillary the wall of which is permeable to at least one chemical species to be detected; (2) a means for delivering at least one fluid medium into the space inside the capillary, the fluid medium comprising at least one reagent that is capable of undergoing a selective chemical interaction with the at least one chemical species to yield at least one optically detectable product; and (3) a means for transferring a content of the capillary to a detector for detecting the at least one optically detectable product, thereby detecting the at least one chemical species.
According to one aspect of the present invention, the detector is capable of quantitatively relating an optical signal that results from the presence of the interaction product to the amount of the chemical species outside the capillary.
In another aspect of the present invention, the optical signal is an absorbance or an emission of electromagnetic radiation having a wavelength in the range of UV to IR (or from about 100 nm to about 1 mm).
A method of the present invention for detecting the presence, determining the location or the spatial distribution, and quantifying an amount of at least one chemical species comprises (1) providing a capillary in an area having the chemical species to be detected, the wall of the capillary being permeable to the chemical species; (2) delivering at least one fluid medium into the space inside the capillary; (3) allowing the chemical species to permeate through the wall of the capillary; (4) transferring a content of the capillary through a sensing element of a detector that is capable of detecting at least one characteristic of the chemical species; (5) measuring a magnitude of the characteristic and a time at which the characteristic is detected; and (6) relating the magnitude of the characteristic to an amount of the chemical species outside the capillary and the time at which the characteristic is detected to the location of the chemical species.
According to one aspect of the present invention, a method of the present invention for detecting the presence, determining the location or the spatial distribution, and quantifying an amount of at least one chemical species comprises (1) providing a capillary in an area having the chemical species to be detected, the wall of the capillary being permeable to the chemical species; (2) delivering at least one reagent into the space inside the capillary, the at least one reagent being capable of reacting or selectively interacting with the chemical species to be detected to yield at least one optically detectable product; (3) allowing the chemical species to permeate through the wall of the capillary and react or interact with the at least one reagent to yield the at least one optically detectable product; (4) transferring the content of the capillary through a sensing element of a detector that is capable of detecting at least one optical signal resulting from the presence of the at least one optically detectable product; (5) measuring a magnitude of the at least one optical signal and a time at which the at least one optical signal is detected; and (6) relating the magnitude of the optical signal to an amount of the chemical species outside the capillary and the time at which the optical signal is detected to the location of the chemical species.
According to one aspect of the present invention, a plurality of optical signals is detected. The times of detection of the plurality of the optical signals provide the spatial distribution of the chemical species along the capillary.
Other features and advantages of the present invention will be apparent from a perusal of the following detailed description of the invention and the accompanying drawings in which the same numerals refer to like elements.